In an uplink multiple-input multiple-output (ULMIMO, Uplink Multiple Input Multiple Output) system, when a user equipment (UE, User Equipment) sends data at each transmission time interval (TTI, Transmission Time Interval), a transport format is selected to send the data to a network side. This transport format is identified by using an enhanced dedicated channel transport format combination indicator (E-TFCI, Enhanced Dedicated Channel Transport Format Combination Indicator). In one TTI, an E-TFCI corresponds to a transmission block size (Transmission Block Size). A mode in which a UE transfers one data block to a base station in a same TTI is referred to as a single-stream transmission mode. A mode in which a UE transfers two data blocks to a base station in a same TTI is referred to a dual-stream transmission mode, where one data block is a primary data block and the other data block is a secondary data block. A data stream corresponding to the primary data block is a primary data stream (primary stream for short), on which a primary precoding vector is used to perform precoding. A data stream corresponding to the secondary data block is a secondary data stream (secondary stream for short), on which a secondary precoding vector is used to perform precoding. A primary pilot and a secondary pilot are respectively transmitted along with the primary data stream and the secondary data stream to estimate an uplink channel.
In the dual-stream transmission mode of the ULMIMO system, the primary data stream and the secondary data stream share a same code channel set and therefore inter-stream interference is generated; however, in the single-stream transmission mode of the ULMIMO system, there is only one data stream and therefore a problem of inter-stream interference does not exist. In a case in which the primary data stream in the dual-stream transmission mode and the data stream in the single-stream transmission mode use same transmit power and experience a same equivalent channel, and receiver end noise is the same, a signal interference noise ratio of the data stream in the single-stream transmission mode is greater than a signal interference noise ratio of the primary data stream in the dual-stream transmission mode.
The prior art provides a selection solution based on an E-TFC (E-TFCI, Enhanced Dedicated Channel-Transport Format Combination, enhanced dedicated channel transport format combination) of a UE side: A UE performs E-TFC selection according to a serving grant (SG, Serving Grant) and a reference E-TFC set that are delivered by a base station, so as to select a corresponding transmission block size. However, in this existing E-TFC selection solution, impact of inter-stream interference is not considered. If this existing data transmission solution is used in the dual-stream transmission mode of the ULMIMO system, a signal interference noise ratio needs to be increased with the help of outer loop power control when the base station demodulates the dual streams. However, a process of outer loop power control is slow; therefore, transmit power on the UE side is wasted and duration in which the base station demodulates the dual streams is prolonged.
The prior art provides another E-TFC selection solution: A base station defines a difference of signal interference noise ratios between the single-stream transmission mode and the dual-stream transmission mode of the ULMIMO system as a channel quality difference caused by inter-stream interference. This existing channel quality difference depends on a receiving environment, and also depends on a base station receiver algorithm. The base station delivers this channel quality difference to a UE and the UE performs E-TFC selection based on this channel quality difference, so as to select a corresponding transmission block size. In a specific implementation of delivery of a channel quality difference, there are the following two implementation solutions:
One solution is that, in the single-stream transmission mode and the dual-stream transmission mode of the ULMIMO system, the base station delivers two reference E-TFC sets. The first set is a reference E-TFC set used in the prior art, which is used for E-TFC selection in the single-stream transmission mode; the other set is used for E-TFC selection for the primary data stream in the dual-stream transmission mode. Then a difference between these two reference E-TFC sets is a channel quality difference. When the UE performs E-TFC selection for the primary data stream, the UE needs to consider this channel quality difference. In this solution, the base station needs to deliver an extra reference E-TFC set for exclusive use by the dual-stream transmission mode. If the base station chooses to deliver the extra reference E-TFC set at a high layer, the delivery is performed at a low frequency. Because inter-stream interference depends on the receiving environment, the delivery at the high layer may not adapt to a change of the receiving environment and cannot reflect a magnitude of inter-stream interference in a current environment, thereby causing a lower feasibility of this solution. If the base station chooses to deliver this extra reference E-TFC set at a physical layer and increase the delivery frequency, because an amount of information about the reference E-TFC set is large, much downlink channel resource needs to be occupied.
The other solution is that, the base station delivers only one reference E-TFC set and the UE uses a same reference E-TFC set, that is, the original reference E-TFC set to perform E-TFC selection in the single-stream transmission mode and the dual-stream transmission mode of the ULMIMO system. However, the base station also sends a grant offset (GO, Grant Offset). This grant offset serves as a channel quality difference and is used to correct an E-TFCI that is selected for the primary data stream in the dual-stream transmission mode. This grant offset does not change transmit power of the primary data stream and is a fixed value delivered by the base station. When the UE performs E-TFC selection for the primary data stream, the UE needs to consider this channel quality difference. In this solution, the UE only needs to deliver one GO in the dual-stream transmission mode. Because an amount of information about the GO is small, the GO may be delivered at a high frequency at the physical layer. However, when the transmit power of the primary data stream is different, the channel quality difference caused by inter-stream interference is different. The grant offset delivered in this solution is unchanged; therefore, this solution is not applied to the E-TFC selection in the dual-stream transmission mode of the ULMIMO system either.